THE LOST RIVERS OF LONDONThe River Tyburn 4b) Buckingham Palace → Pimlico

To fully remove the lower reaches of the river Tyburn, its waters were dropped into a brick sewer in the early 18th century. Rather than tracing the route of the river towards Westminster, the new culvert instead headed south from Buckingham Palace and made for the Thames at Pimlico. This was the King's Scholars' Pond Sewer, named after Westminster School's ablest pupils (which is perhaps not the way they'd prefer to be remembered). Soon after leaving the royal residence it today passes beneath more mundane backstreets, then past the big new shopping/office complex at Cardinal Place. I'm guessing it flows beneath Billy Elliot at the Victoria Palace Theatre [photo], which is something best not considered when you're sitting in the stalls. The sewer's also causing problems with the construction of a new ticket hall for Victoria tube station at Bressenden Place, because the brown tube isn't as far below the ground as engineers would like.

Next up, an unexpectedly grim back passage. That's King's Scholars' Passage, a lengthy access road squashed between six-storey brick cliffs round the back of Vauxhall Bridge Road [photo]. If you can ever avoid visiting, do. This emerges outside the Queen Mother Sports Centre (no, she never popped by for an Age Vitality Workout, it's merely named after her). The sewer then follows the curve of Tachbrook Street, which is delightfully Georgian-terrace on one flank and depressingly postwar-block on the other [photo]. Nearly there. One final stretch beyond Pimlico station, beneath the Tachbrook Estate, and we're at the Thames.

Unusually for a lost river, the bottom of the Tyburn is really obvious. Two houses stand out beside the busy riverside dual carriageway, being rather older than the modern piles to either side [photo]. One's Rio Cottage, labelled with a plaque announcing it was built in 1832 "as part of Kingschoole Sluice". Nextdoor at number 140C is Tyburn House - similarly old looking but with an extra storey on top. Between them they guard the exit to the King's Scholars' Sewer, which disgorges (when necessary) beneath one resident's back window [photo]. They can even nip down a metal staircase at low tide to their own pebbly beach, if they're brave enough. And in case all the clues aren't obvious enough, a slab of slate affixed to the riverside path charts a rundown of the Tyburn's progress all the way from Shepherds Well to Tachbrook Street [photo]. Journey's end, job well done. [photo]